A. Field of the Invention
The present invention relates to an apparatus for precisely positioning an ultrasonic bonding tool or similar implement relative to a workpiece. More particularly, the invention relates to a micro-manipulator apparatus which includes an input position controller mechanism coupled to an output follower mechanism effective in positioning the tip of an ultrasonic or similar wire bonding tool at precisely determinable locations relative to a microcircuit or similar workpiece, moving the tool tip into contact with the workpiece to form a bond, and withdrawing the tool tip upon completion of a bond.
B. Description of Background Art
A large variety of scientific procedures, medical procedures and industrial processes require the use of a type of apparatus referred to generally as a micro-manipulator for the precise positioning of a tip of a tool or instrument relative to a small workpiece or other such object. For example, the manufacture of electronic components such as integrated microcircuits requires the use of a micro-manipulator-type apparatus, for the following reasons.
Integrated circuits are fabricated from thin slices of a semi-conducting material such as silicon, germaniun, gallium arsenide, or other III-IV compounds, i.e., compounds of elements from columns three and four of the periodic table. The slices are cut into small squares or rectangles referred to as chips or dice, ranging in size from squares about 100 mil (0.100 inch) on a side to several hundred mils. Transistors, diodes, resistors and interconnecting circuit paths are formed on each chip or die by diffusing impurities into selected regions of the die to produce a desired electrical conductivity. Various conducting paths and insulated layers are then deposited on the chip.
After a semi-conductor chip or die has been fabricated as described above, it must be attached to a base or carrier. A lid is then sealed to the base to form a package or container which protects the delicate die from damage. Prior to attaching the lid to the carrier which supports the die, conductive pads provide input and output conductive paths to the die must be electrically interconnected to more robust leads or terminals which extend outward from the carrier. These interconnections are customarily made using fine aluminum or gold wires. The wires are ultrasonically or thermo-sonically welded to the pads and external leads by a bonding tool that applies ultrasonic energy, or a combination of heat and ultrasonic energy, to a bonding site. Since the connection pads of a microcircuit are extremely tiny and closely spaced, great precision is required in positioning the tip of a bonding tool relative to the microcircuit.
Responsive to the need for an apparatus capable of precisely positioning the tip of an ultrasonic transducer to form wire bonds on microcircuit chips, the present inventor invented a micro-positioner apparatus which employs a novel pantograph-type manipulator input mechanism. That apparatus, which was disclosed in the present inventor's U.S. Pat. No. 3,474,685 and issued on Oct. 28, 1969, has proven to be highly effective in performing its intended functions, and wire bonding machines employing the novel design concepts including the pantograph mechanism disclosed in that patent are widely used throughout the electronics industry. However, the present inventor found that certain aspects of the micro-positioner disclosed in the 3,474,685 patent might be improved upon. For example, the allowable working or throat depth of the ultrasonic tool tip would preferably be larger for certain bonding applications.
Also, the use of offset pivotable mountings for the transducer tool support plate would desirably be minimized, thereby minimizing the requirement for springs to counter balance unbalanced forces exerted in supporting the tool support plate by offset mountings. Moreover, it would be desirable to have a micro-positioner apparatus in which various ultrasonic transducers and other bonding tool accessories such as wire spooling mechanisms, some of which might be substantially heavier than conveniently supportable by prior art micro-positioners, could be used. Such a need arises, for example, in bonding the heavier wires required for connection to certain electronic components such as wound coils and disk drive components. In response to those considerations, the present inventor disclosed a Micro-positioner For Ultrasonic Bonding, U.S. patent application Ser. No. 08/773,637 filed Dec. 24, 1996, now U.S. Pat. No. 5,871,136.
In that patent application the present inventor disclosed a micro-positioner apparatus having a pantograph-like input manipulator mechanism, and a follower mechanism coupled to the input manipulator mechanism by a ball joint and supporting an ultrasonic transducer housing and bonding tool on a tool support plate. The tool support plate is longitudinal slidably mounted on a tool support guide plate, allowing fore and aft motion of the tool tip. The tool support guide plate is in turn pivotably supported by a yoke having a yaw pivot bearing which allows lateral motion of the tool tip. The yoke is in turn supported by a pitch pivot bearing having a horizontally disposed pivot axis, thereby permitting pivotal motion in a vertical plane of the yoke, tool support plate, and tool tip. By a suitable choice of spacings between the pivot axes of the pantograph input manipulator mechanism, support bearings and ball joint, the tip of the bonding tool is caused to move in coordinate directions of a second coordinate system containing the tool tip in precisely scaled ratios of corresponding motions in a first coordinate system of an input control knob on the input manipulator mechanism. The combination of a longitudinally slidable tool support plate with two pivot bearings orthogonal to each other and to the slide axis, provides a micropositioner apparatus which has both a rugged construction capable of supporting heavy loads on the tool support plate, and a substantial throat depth. In a preferred embodiment of the disclosed apparatus, the longitudinal slide axis of the tool tip, and the pivot axes of the pitch and yaw pivot bearings all intersect at a common point, thereby assuring completely orthogonal motions of the tool tip in three orthogonal coordinate directions that are precisely scaled fractions of corresponding input control knob motions.
The present invention was conceived of to provide a micro-manipulator for ultrasonic bonding applications having a manipulator input mechanism and tool holder follower mechanism which are both pendent from an overlying support structure, thereby affording a work space of potentially unlimited lateral extent below the apparatus. Among other advantages, the large work space can accommodate workpieces located on a conveyor belt disposed below the apparatus.